Do pesticides and herbicides harm gut flora?

Expert response from David Oppenheimer

Associate Professor, University of Florida

Monday, 12/10/2015 13:32

Technically, pesticides are compounds that are meant to kill pests. This is a very broad definition, since a "pest" in one case, can be a beneficial organism in another case. Pesticides include substances that kill plants (herbicides), fungi (fungicides), insects (insecticides), bacteria (bacteriocides, or antimicrobials) and, well you get the picture. 

Most of these pesticides have very limited effect on organisms other than their intended targets. For example, the common herbicide glyphosate is very effective at killing plants, but is even less toxic to animals than table salt. Currently, 

the U.S. Environmental Protection Agency (EPA), and other regulatory agencies have strict limits on where, when, what and how much of particular pesticides can be applied to crops or livestock. Crops and livestock are routinely monitored to make sure that the residues on and in the crops are at acceptable levels such that they are not toxic to humans.

Now on to the gut flora issue. First, the gut microbiome is a very complex population of microbes. And is a large population that is always changing. Literally one third of human fecal material is microbes. There are actually more bacterial cells in your gut (by number) than there are of all other cells in your body. That's a lot of bacteria! Since your gut is constantly moving stuff through it, the population of bacteria can change depending on lots of factors. Many bacteria live in close association with your intestinal wall, and are greatly affected (and can affect) the immune system. Of course antibiotic treatment can affect the numbers and types of microbes in the gut as can treatment with many other drugs (or supplements) that affect your physiology. 

Now, on to the connection between pesticides and gut flora. Copper sulfate is one of the most widely used pesticides by organic farmers (more than 30 percent of organic farms use this pesticide). Interestingly, some of the sulfur that organic farms use comes from the scrubbers in the smoke stacks on coal-fired power plants (an interesting factoid that I recently learned). But I digress. Copper sulfate is also an antimicrobial that is fed to pigs so that they put on weight faster. In pigs, copper sulfate can alter the microbiome, but the changes depend on lots of other factors including age of the pig, duration of the treatment, dosage of the copper sulfate, and other things. I recently attended a seminar where data on microbiome was shown for individual people over time. This was not in response to any treatment, it was just to see if the microbiome changed. Interestingly, in some people, the microbiome changed a lot, in others hardly at all. In the ones where the microbiome changed a lot, there was no evidence of any disease or ill-health. Currently it is not clear that all changes in the microbiome are indicators of ill-health. Some changes may be "natural". 

Therefore, broadly speaking, the changes to your gut flora, if any, by the small amounts of pesticides that you might consume from eating crops or livestock treated with pesticides (organic or conventional), are unlikely to cause you any harm. So the bottom line is, don't worry, organic food is safe to eat.

Expert response from David Oppenheimer

Associate Professor, University of Florida

Monday, 12/10/2015 13:32

Technically, pesticides are compounds that are meant to kill pests. This is a very broad definition, since a "pest" in one case, can be a beneficial organism in another case. Pesticides include substances that kill plants (herbicides), fungi (fungicides), insects (insecticides), bacteria (bacteriocides, or antimicrobials) and, well you get the picture. 

Most of these pesticides have very limited effect on organisms other than their intended targets. For example, the common herbicide glyphosate is very effective at killing plants, but is even less toxic to animals than table salt. Currently, 

the U.S. Environmental Protection Agency (EPA), and other regulatory agencies have strict limits on where, when, what and how much of particular pesticides can be applied to crops or livestock. Crops and livestock are routinely monitored to make sure that the residues on and in the crops are at acceptable levels such that they are not toxic to humans.

Now on to the gut flora issue. First, the gut microbiome is a very complex population of microbes. And is a large population that is always changing. Literally one third of human fecal material is microbes. There are actually more bacterial cells in your gut (by number) than there are of all other cells in your body. That's a lot of bacteria! Since your gut is constantly moving stuff through it, the population of bacteria can change depending on lots of factors. Many bacteria live in close association with your intestinal wall, and are greatly affected (and can affect) the immune system. Of course antibiotic treatment can affect the numbers and types of microbes in the gut as can treatment with many other drugs (or supplements) that affect your physiology. 

Now, on to the connection between pesticides and gut flora. Copper sulfate is one of the most widely used pesticides by organic farmers (more than 30 percent of organic farms use this pesticide). Interestingly, some of the sulfur that organic farms use comes from the scrubbers in the smoke stacks on coal-fired power plants (an interesting factoid that I recently learned). But I digress. Copper sulfate is also an antimicrobial that is fed to pigs so that they put on weight faster. In pigs, copper sulfate can alter the microbiome, but the changes depend on lots of other factors including age of the pig, duration of the treatment, dosage of the copper sulfate, and other things. I recently attended a seminar where data on microbiome was shown for individual people over time. This was not in response to any treatment, it was just to see if the microbiome changed. Interestingly, in some people, the microbiome changed a lot, in others hardly at all. In the ones where the microbiome changed a lot, there was no evidence of any disease or ill-health. Currently it is not clear that all changes in the microbiome are indicators of ill-health. Some changes may be "natural". 

Therefore, broadly speaking, the changes to your gut flora, if any, by the small amounts of pesticides that you might consume from eating crops or livestock treated with pesticides (organic or conventional), are unlikely to cause you any harm. So the bottom line is, don't worry, organic food is safe to eat.